Lithium cells have been subject to intensive development efforts during the last two decades, and enabled existence of many portable devices. The increased demand for higher capacity and safety of lithium accumulators is now a limiting factor in development of many applications including the replacement of lead-acid accumulators for lithium accumulators with higher voltage in automobiles, or large accumulators for electromobiles.
Main part of currently produced rechargeable lithium accumulators are based on thin film electrodes where a mixture of active materials, conductive carbon and organic binders is sprayed or laminated in a thin layer onto a foil of conductive material, usually aluminum or copper, functioning as current collector. The thickness of such planar electrodes usually ranges from several microns to one hundred microns. The positive and negative electrodes are stacked up and separated from each other by a thin intermediate layer consisting of an electrically non-conducting material, typically a perforated foil of an organic polymer-separator. The stacked electrodes separated by separators are subsequently pressed down, closed into a case and the free space is filled up by electrolyte. A non-aqueous solution of lithium salts is frequently used for electrolyte.
The object of EP1777761A2 offers a solution, which is to increase the safety of thin film planar accumulator at higher temperatures by means of two separator layers, whereby one layer is constituted of electrolyte salt, binder and an organic powder (1-40 m m) and the second layer comprises a ceramic powder (5-30 m m). The thickness of electrodes is only several microns and the solution thereof does not enable further reduction of the amount of separators, thus increasing both the volume and the capacity of accumulator cells.
US2008038638A1 a JP2000090922 disclose the formation of a composite matrix having a defined porosity and capable to intercalate lithium, whereby such matrix is composed of particles able to form lithium alloys and an inactive material (covalent inorganic compounds).
PCT application WO2010031363 presents a lithium accumulator consisting either of a shell in which the mutually isolated electrodes are pressed into, or of a stack of metal frames arranged above each other, where each frame comprises an orifice, in which a thick-walled, so called three dimensional (3D) electrode is placed. The electrodes of opposite polarity are separated by separators and the frames of opposite polarity are insulated from each other. The electrodes have spatially distributed electron conductive component with a homogenously mixed active material capable to absorb and release lithium in the presence of electrolyte. The lithium accumulator is prepared by successive compressing a first electrode layer, separator and the second electrode, whereupon the housing is filled up by electrolyte, closed and the poles of the identical electrodes are interconnected. The accumulators of higher capacity comprise additional current collectors between the sandwich electrodes. The described electrode composition, arrangement and preparation thereof are well suitable for 3D electrodes, which enable the accumulator to achieve high volumetric capacity. Nevertheless, this advantage is accompanied by a longer charging period and also by increased volume and weight of the accumulator and decreased active area on account of frames.